The process for valve sizing can be confusing. There are numerous variables in oil and gas controls, and an array of options to deal with those variables. In this piece we’ll be covering the three most important factors in selecting a control valve:
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- High vs. Low Pressure Control Valves
- The Meaning of Valve Cv
- How Valve Cv Affects Trim Sizes
1. High Pressure vs. Low Pressure control Valves
The first question you need to ask when valve sizing is “What is my pressure?”
- For gas applications, if your pressure is more than 300psi, you need a high pressure control valve. If it’s less than 300 psi, you can likely use a low pressure regulator.
- For liquid applications, if your pressure is more than 500psi, you need a high pressure control valve. If it’s less than 500 psi, you can use a lever-operated or pneumatic dump valve.
While it sounds obvious to choose high pressure valve for high pressure application, there is another key factor you have to consider: Calculated Cv.
2. The meaning of valve Cv
The second question you need to ask when valve sizing is “What is my Cv?”
Cv is the number of gallons of water that will pass through a given flow restriction at a 1 psi differential.
Put simply, you can think of it as the orifice size of a valve.
To calculate your Cv, plug your flow conditions into the Kimray sizing calculator. You can also use this video guide to learn how to use this sizing calculator.
Now let’s look at two examples of how Cv helps us with sizing control valves.
Example 1
- Your pressure is less than 300 psi and your required Cv is 3 or greater.
- In this case, a low pressure regulator should work for a gas application, while a low pressure control valve or lever operated liquid dump valve will work for a liquid application.
Example 2
- Your pressure is still less than 300 psi, but your required Cv is less than 3.
- In this example. you should use a Stem Guided High Pressure Control Valve because it can meet the small Cv requirements.
It may sound counter-intuitive to use a high pressure control valve for low pressure application, so let’s dig a little further…
3. how valve Cv affects Valve Trim Sizes
Kimray low pressure valves and regulators come with 2 simple trim options—full port or reduced port—and might be too big for the small flow rates.
Meanwhile, Kimray 2” stem-guided high pressure control valves come with 9 trim options ranging from ¼” up to 1”. (Our 1” stem-guided valve trim options range from 1/8” – ½”.)
Stem-guided valves have tight Cvs—from .34 to 21. They can handle low flow as well as high pressure drop applications where you have a small Cv requirement.
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For larger Cvs and higher pressures, Kimray’s Cage Guided High Pressure Control Valves are full port valves with a Cv range of 28.6 to 1,091.
While our stem-guided valves are available only in 1” and 2” sizes, our cage-guided valves are available in 2" through 10".
Can I Change My Valve Trim?
We’ve now walked through control valve selection. But what about if you have valves on an existing well and conditions change?
A key benefit of Kimray control valves is their versatility. For example, If you resize your valve with the new conditions and the calculated Cv does not fit the trim on your existing stem-guided valves, you can swap the trim for a different size.
This will keep you from having to change your piping to fit a larger or smaller valve.
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What is Valve Cv?
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Control valves play an important role in various process industries. They are designed to control the flow of fluids in a system. They are designed to start and stop as well as throttle the fluid flow to ensure efficient process operation. Owing to their increasing use in process industries, today, it is easy to find these valves in different specifications. This large selection may be confusing to users who are purchasing it for the first time. There are several factors to be considered when making a selection. This post aims to ease the control valve selection by providing a few easy-to-follow tips.
What Are the Different Types of Control Valves?
Control valves are differentiated based on their designs and other characteristics. The following are a few important types of control valves in use today:
- Linear globe valves: These valves are made of cylindrical or disk plug element, and have a spherical body and a stationary ring seat. Linear globe valves allow easy access to internal elements, and they are used to regulate the flow of a variety of fluids.
- Linear angle valves: The control valves are designed for severe applications, which may have large noise, flashing, and flow rates.
- Rotary valves: In this type of valve, the liquid flow is regulated through the rotation of passages present in a transverse plug. These valves are ideal for applications, where fluids being transferred may contain solids. In many applications, rotary valves serve as a replacement for globe and angle valves. These valves are designed for severe applications, and they are suited for applications where cleanliness is not mandatory.
- Linear three-way control valves: These control valves feature two outlets and one inlet or vice-versa. Linear three-way control valves are used for applications, where liquids may be involved. They enable easy mixing of liquids from two different pipes into a single pipe. These valves can be found in water chillers, fan coils, air handling units, and so on.
5 Factors to Consider When Selecting Control Valve for Your Process
The purpose of this section is to provide you points that will ease the control valve selection process for your next project.
- Fluid to be Transferred: What type of fluid will be transferred at your processing plant? The control valves are designed for controlling the flow of media such as natural gas, compressed air, steam, liquefied petroleum, gasoline, hydraulic fluid, slurry, and water. So, it needs to be ensured that the valve works perfectly for all these fluids.
- Material Grades: As said earlier, today, it is easy to find the industrial valves in various stainless steel material grades such as ASTM, ASTM A217 grade, A216 grade WCC, ASTM A351 CF8M, and so on.
- Flow Control Characteristics: Address the maximum and minimum or acceptable temperature range of the fluid to be transferred. Also, address the minimum and maximum inlet and outlet pressures that a valve is expected to handle. This will help you understand the flow control characteristics of the valve. Ensure that the valve chosen offers consistent control across various temperatures. Also, they meet equal or linear percentage or several other characteristics. Understand that these flow characteristics will vary across different processes, and the valve must be able to assure stability across all conditions.
- Compatibility with Remote Systems: Owing to the criticality of the process environment, many processes require remote control and monitoring. It is important to ensure that the valve chosen complies with the remote process management systems.
- Rugged Construction: Most industrial processes are conducted in ambient, harsh environments; so, if the chosen valve is unable to meet these diverse requirements, then it may fail to serve the purpose. You need to check if the valve can withstand the extremes and minimums as well as upset conditions, and can operate virtually.
In addition to the above-discussed tips, you can discuss your requirements with the manufacturer. Whenever you are considering these valves for your project, ensure that they are sourced from a reliable supplier like The Transmitter Shop. The company provides a new surplus, reconditioned, and factory new control valves.
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